In some cases, law-enforcement or security agencies may wish to monitor communication over a computer network, such as the Internet, in order to identify activities taking place on the computer network. A challenge in doing so, however, is that many applications use encrypted protocols, such that the traffic exchanged by these applications is encrypted. Examples of such applications include Gmail, Facebook, and Twitter. Examples of encrypted protocols include the Secure Sockets Layer (SSL) protocol and the Transport Layer Security (TLS) protocol.
Conti, Mauro, et al. “Can't you hear me knocking: Identification of user actions on Android apps via traffic analysis,” Proceedings of the 5th ACM Conference on Data and Application Security and Privacy, ACM, 2015, which is incorporated herein by reference, describes an investigation as to which extent it is feasible to identify the specific actions that a user is doing on mobile apps, by eavesdropping on their encrypted network traffic.